This invention relates to a method and apparatus for calibrating a particulate sampler system used in quantifying particulates from vehicle emissions.
Particulate sampler systems are used to quantify emission particulates from, for example, diesel engines for vehicles. The systems are used for engine development and to ensure compliance with governmental regulations concerning emissions of particulate matter.
The particulate sampler system must be calibrated to ensure its accuracy so that test results are reliable. The test procedures, calibration, and accuracies are often specified by various regulations and standards, such as ISO 16183. It is desirable to have better than five percent accuracy.
One typical particulate sampler system includes a probe that obtains a sample from an exhaust source. The sample is diluted using a diluent such nitrogen that flows through a dilution mass flow controller to mix with the exhaust sample in a dilution tunnel. The diluted sample flows through a diluted exhaust mass flow controller from which the diluted exhaust sample is then collected in a filter. The particulate matter from the exhaust source is calculated, in part, by determining the volume of sample collected. The mass flow through the dilution mass flow controller is subtracted from the mass flow of the diluted exhaust mass flow controller.
Prior to any testing, the mass flow controllers are calibrating using a laminar flow element (LFE), which is arranged in the particulate sampler system in place of the probe. Since the diluted exhaust mass flow controller is calibrated independently of the dilution mass flow controller, any calibration error in the diluted exhaust mass flow controller is transferred to the dilution mass flow controller during the calibration with the LPE. This results in what is referred to as a transfer error which can result in an accuracy that is worse than the desired five percent. What is needed is an improved calibration apparatus and procedure to improve the accuracy of the particulate sampler system.